Alloy adapted for furnace components

ABSTRACT

A dispersion strengthened nickel-base alloy containing correlated percentages of chromium, yttria, aluminum, titanium and carbon, the alloy being adapted for use in the fabrication of components for high temperature furnaces.

United States Patent [191 Merrick 1 Nov. 25, 1975 1 ALLOY ADAPTED FORFURNACE COMPONENTS [75] Inventor: Howard Francis Merrick, Suffern,

[73] Assignee: The International Nickel Company,

Inc., New York, N.Y.

[22] Filed: Jan. 22, 1973 [21] App]. No.: 325,887

' [52] US. Cl. 148/32; 29/1825; 75/171;

' [51] Int. Cl. C22C 19/05 [58] Field of Search 75/171, 170, .5 AC, .5BA, 75/.5 BC, 205; 148/32, 32.5, 11.5 F, 126; 29/1825; 139/425 PrimaryExaminer-R. Dean Attorney, Agent, or Firm-Raymond .1. Kenny; Ewan C.MacQueen [57] ABSTRACT A dispersion strengthened nickel-base alloycontaining correlated percentages of chromium, yttria, aluminum,titanium and carbon, the alloy being adapted for use in the fabricationof components for high temperature furnaces.

[56] References Cited UNITED STATES PATENTS- 4 Claims, 1 Drawing Figure1,609,849 12/1926 Wagner 34/208 (ea /15x 54 z fi g d) N E F W4! /5 6- iM {/3591 m 0 .U fizscy 0 ALLOY ADAPTEI) FOR FURNACE COMPONENTS Thesubject invention is addressed to high temperature alloys, andparticularly to novel cold workable, dispersion-strengthenednickel-chromium alloys capable of being fabricated into structuralcomponents for use in high temperature furnaces.

As is known, nickel and nickel-base alloys have found extensive use incombatting the destructive effects occasioned by high temperature. Forexample, in respect of furnaces of the heat treating and sinteringtypes, wire mesh conveyor belts are fabricated from such alloys byvirtue of the fact that the alloys offer reasonably goodstrength'characteristics and resistance to oxidation at elevatedtemperature. Such attributes notwithstanding, it is considered that thewire mesh belt industry would respond favorably to a material ofincreased temperature capability. This is not to say the presentinvention is intended to be restricted to wire mesh belt fabrication.

During the course of my investigation, some consideration was given toTD Ni and'also to TD NiCr, alloys of the dispersion strengthening type.TD Ni does possess good high temperature strength and is relatively coldworkable; however, it suffers from lack of oxidation resistance. On theother hand, while the resistance to oxidation of TD NiCr is acceptable,its strength characteristics leave something to be desired, this byreason of difficulties encountered in respect of using practical,conventional cold working procedures while retaining a fibrous grainstructure, particularly one in which the aspect ratio exceeds about 5 or7 to 1. And good cold working characteristics are rather indispensableif such products as wire and sheet are to be produced for subsequentfabrication.

In any case and in accordance with the present invention, it has beenfound that highly oxidation resistant, cold workable alloys can beproduced and which are capable of delivering high strength at elevatedtemperature, provided a special correlation is maintained among acombination of certain constituents, including nickel, chromium, yttriaand other elements as disloys, the upper level preferably being notgreater than about 0.45%, up to 0.5 or 1% each of aluminum and titanium,up to 0.1% carbon and the balance essentially nickel. As will beunderstood by those skilled in the art,

in referring to nickel as constituting the balance or balanceessentially of the alloys, other elements may be present which do notadversely affect the basic characteristics of the alloys.

In carrying the invention into practice, the chromium level should notfall below about 12.5%, less oxidation resistance be impaired. Chromiumpercentages much above 20% tend to introduce other problems, notablyundesirable limitations with regard to cold working procedures incombination with grain structure defects as will be discussed in greaterdetail herein. A chromium range of about 13 to 18% is deemedparticularly beneficial. r

Careful control should be exercised in respect of the yttria content,particularly in relation to chromium. Though a yttria level of up topossibly 0.5% (volume) might be tolerated, if yttria is present to theexcess,

'cold working problems can be introduced. Although in point fallingwithin the area encompassed by the rectangle ABCD of the accompanyingdrawing. In this regard, it is considered that if the upper yttrialevels are used concurrently with the higher chromium contents, a lesseramount of cold work can be imparted to the alloys than otherwise wouldbe the case. Thus, to cold draw an alloy containing about 0.45 to 0.5%yttria (volume) and 20% chromium, results in a situation in which notmuch more than about the cold reduction of 10% can be obtained whileretaining the necessary elongated grain structure upon high temperatureexposure essential to strength. This places a heavy burden onfabricability. It is of benefit that the yttria and chromium beproportioned to give a point within area EFGH of the drawing.

In seeking optimum results in terms of cold working, aluminum andtitanium should not exceed about 0.5%, respectively, a range of about0.1 to 0.5% being satisfactory for each. Carbon should not exceed about0.075%. As to other elements, iron is unnecessary although amounts up tosay 5 or 10% can be present. Oxygen and nitrogen should preferably notexceed about 0.5% and 0.2%, respectively.

In order to obtain a fine, uniform yttria dispersion throughout thealloy matrix, the alloys should be prepared by the mechanical alloying"technique as described in U.S. Pat. No. 3,591,362. This is a process inwhich-*a charge of constituent powders is subjected to dry, intensivehigh energy milling in a machine such as an attritor whereby the initialconstituents become intimately interdispersed to form dense andexceptionally homogeneous composite alloy powder particles. thecomposition of which correspond to the respective percentages of theconstituents found in the original charge. For purposes of illustrationand using a 4 gallon attritor, a ball-to-powder ratio of 10:1 to 30:1(volume) can be used at an impeller speed of about 250 to 300 rpm for aperiod of 15 to 25 hours under a nitrogenoxygen atmosphere. In using52100, through hardened balls, it should be borne in mind that iron willbe likely introduced into the final composite particles. If iron isundesired, nickel carbonyl balls might be preferred.

It is important that the alloys ultimately be characterized by amicrostructure of coarse, elongated grains as opposed to, for example, afine grain structure. In the latter case, stress rupture strength at thetemperatures under consideration is virtually nil. To explainin thenormal course of processing, the composite product particles are hotconsolidated, as by hot extrusion, temperatures of 1800 to 2100F. beingused together with extrusion ratios of 10:1 to 25:1. Subsequent tofurther hot working, if any, the alloys are subjected to a germinativegrain growth heat treatment overthe range of about 2350 to about 2500F.for about as to 1 hour.

3 Should the temperature be too low, the fine grain structure of the'hotconsolidation treatment will persist with attendant inferior properties.Incipient liquation difficulties will ensue should the grain growthtreatment be of Alloy 2 vs. Alloy I, particularly room temperatureductility, was in large part due to the much higher oxygen content.

Stress rupture properties were also determined in retoo high. spect ofAlloys 1 and 2 and the results are given in In order to give those abetter appreciation of the Table III. (Tests were not conducted on AlloyA owing present invention, the following data are given: to theinherently low tensile strength thereof). In the A series of Alloys 1, 2and A (outside the invention) course of the stress rupture evaluation,specimens were Table I, was prepared by the mechanical alloying profirsttested at a selected stress level for approximately cess, 123 carbonylnickel powder of minus 325 mesh, 100 hours. Iffailure did not occurwithin this given time 9999% chromium powder minus 100 plus 200 mesh,period, the stress was increased and allowed to creep a 300M iron powderminus I00 mesh, a nickel-aluminum further 100 hours. This procedure wasrepeated until a master alloy minus 100 mesh and fine yttria, werestress level was obtained leading to rupture in less than blended into acharge and placed in a 4-gallon attritor. 100 hours. The impeller speedwas maintained at about 250 rpm, TABLE In the milling being conductedfor a period of about hours. A ball-to-powder ratio (volume) of about :1Life Alloy F. ksi hrs. /1 "/1 was used wlth a nitrogen-air atmospherebeing mamtained during processing. 2050 8 Unbm' ken The composite alloypowders so produced were then 20 99 Unbw. sealed in a cylindrical mildsteel can and extruded to 1 1 34 3 4 ken 9 8 three-fourths inch bar at atemperature of 2000F.,'an 2 2050 12 5 Unbm extrusion ratio of 22:1 beingused. ken

13* 37.8 7 24 TABLE I 25 g "stress on specimen raised to shown valueChemical Composition Cr Y,0,* Al Fe N c Ni Alloy Both Alloys 1 and 2responded very well in this test. 1 13,1 Q22 Q24 0 034 48 005 M In thisconnection, an acceptable wire belt alloy should i 5-: 85; 8%; 8-83;8-8;; 33- afford a 100 hour rupture strength at a temperature of 2050F.'at a minimum stress level of 6,000 psi. This was far surpassed by eachof the alloys in question. mmamed 0259' Alloys 1, 2 and A were testedfor response to cold working. Specimens were first extruded, annealed atp extrusion, bar Stock Specimens were annealed 35 2400F. and thensubjected to various percentages of for 1 hour at temperatures of 2300?and cold reduction. As a result, it was determined, for ex- 2500F. toascertain the temperatures at which germil h All 1 o ld b cold reducedby a factor native grain growth would occur. At 2300F., none of f 86% ih recourse to |i i the alloys manifested y appreciable evidence of grainstanding that Alloy l was susceptible to such a high degrowthwhenannealed at 2400 and 250001;, gree of cold deformation, a fibrous grainstructure did ever, both Alloys 1 and 2 were Characterized y a notdevelop upon subsequent annealing at 2400F. Fursired coarsemicrostructure. In the case Of Alloy l, the they attempts to develop thedesired grain tructure by Structure Was more of a by grain yp Whereasthe annealing at various temperatures were unsuccessful. grains wereelongated in respect of Alloy 2. In contrast, H i w s found that withlower percentages of Alloy A was incapable of FeSPOI'IdirIg 10 treatmentand cold reduction, an acceptable and satisfactory grain exhibited anundesired fine-grain, equiaxed structure. structure could be produced,the alloy being amenable Reported in Table below are the tensileProperties to recrystallization. In this connection, it wasdeterdetermined at both room temperature and fOI' mined that 1 could becold reduced approxieach of the three alloys as extruded and annealedfor l mateiy 40 to 45% whil i i in a iform fibrous h a 240 grainstructure. It should be mentioned that fine grains TABLE II 70F. 2050F..2 Y.S. U.T.S. E1. R.A. .2 Y5. U.T.s. El. R.A. Alloy ksi ksi 7: 71 ksiksi 7: k

It will be observed that both alloys 1 and 2 exhibited were developingat the boundaries of the coarse fibrous excellent tensilecharacteristics including both strength grains at a cold reduction ofapproximately 44%. This and ductility not only at room temperature, butmore does permit regions of inhomogeneity to develop. importantly, atelevated temperature. Quite apart from With regard to Alloy 2, it wasnot receptive to cold the fact that Alloy A was characterized by anundesirworking to the extent of Alloy 1. It was determined that ablefine, equiaxed microstructure, it greatly suffered in respect of tensilestrength, notably at 2050F. This occurred notwithstanding the relativelyhigher yttria level. It is also considered that the lower ductilitylevel a maximum cold reduction of approximately 36% was obtainable inthe absence of re-annealing. Recrystallization to a fine equiaxed grainstructure occurred upon annealing after a cold reduction of less than20%. This alloy contained a higher chromium-yttria level than didAlloy 1. As above indicated, the chromium-yttria correlation should mostadvantageously fall within the area EFGH of the drawing.

Tabulated in Table IV are the tensile and stress rupture resultsobtained for Alloys 1 and 2 as a consequence of cold reduction (CR) andthen annealing at 2400F.

TABLE IV Tensile Properties UTS El. ksi

.2% YS ksi Stress Alloy Condition ksi it will be understood thatmodifications and variations of the invention may be resorted to withoutdeparting from the spirit and scope thereof as those skilled in the artwill readily understand. Such are considered to be within the purviewand scope of the invention and appended claims.

I claim:

1. A cold worked dispersion strengthened mechani- Stress-RuptureProperties Life El. hrs.

1 l4 Unbroken 12 1 l5 Unbro ken 9.6

nil 1.

nil

nil 75 *Stress on specimen raised With regard to the data immediatelyabove, the tensile tests for Alloy 1 show an increased strength levelover that determined in the extruded and annealed condition (Table 11).Material cold drawn 24% and then annealed at 2400F. also exhibitedexcellent creep rupture strength at 2050F. The tensile properties of thematerial cold drawn 44% and annealed are somewhat lower, with the stressrupture results being somewhat mixed. It is thought that this behavioris attributable to the fact that upon annealing after the 44% cold work,some fine grains developed. This in turn would subvert stress rupturecharacteristics. The fine grain structure was responsible for the poorstress rupture and tensile properties of Alloy 2.

- ature each 24 hours. Oxidation was measured by weight loss in both theundescaled and descaled conditions. Alloy 1 underwent a loss of 2.92mg/em in the undescaled condition and 8.14 mg/cm descaled. The

' corresponding losses for Alloy 2 were 2.88 and 7.75

mglcm respectively. These results are considered quite attractive incomparison with currently used alloys (Fe--Ni-19 Cr and Fe-35-Ni-l9Cr(Cb stabilized). In a carburization test at 2012F. in H -2% CH for aperiod of 5 hours, Alloys 1 and 2 were not as good in comparison withthe same alloys.

cally alloyed composition suitable for use in the fabrication ofcomponents for high temperature furnaces and consisting essentially offrom about 12.5 to 20% chromium, a small but effective amount of-yttriasufficient to enhance the strength characteristics of the alloy, theupper level being up to 0.45% by volume, up to 1% aluminum, up to 1%titanium, up to 0.1% carbon, and the balance essentially nickel.

2. A cold worked, dispersion strengthened mechanically alloyedcomposition suitable for use in the fabrication of components for hightemperature furnaces, said alloy being characterized by a microstructure(i) substantially devoid of fine grains, (ii) in which the grains arecoarse and elongated, and (iii) in which the aspect ratio of the grainsis at least 5:1, said alloy consisting essentially of about 12.5 to 18%chromium, about 0.175 to about 0.45% yttria, the chromium and yttriabeing correlated so as to represent a point falling within the area ABCDof the accompanying drawing, up to 1% aluminum, up to 1% titanium, up to0.1% carbon and the balance essentially nickel.

' 3. An alloy in accordance with claim 2 in which the chromium andyttria are correlated so as to represent a point falling within the areaEFGH of the accompanying drawing.

4. As a new article of manufacture wire mesh belts for use in hightemperature furnaces are formed from an alloy having a composition asset forth in claim 1.

1. A COLD WORKED DISPERSION STRENGTHENED MECHANICALLY ALLOYEDCOMPOSITION SUITABLE FOR USE IN THE FABRICATION OF COMPONENTS FOR HIGHTEMPERATURE FURNACES AND CONSISTING ESSENTIALLY OF FROM ABOUT 12.5 TO20% CHROMIUM, A SMALL BUT EFFECTIVE AMOUNT OF YTTRIA SUFFICIENT TOENHANCE THE STRENGTH CHARACTERISTICS OF THE ALLOY, THE UPPER LEVEL BEINGUP TO 0.45% BY VOLUME, UP TO 1% ALUMINUM, UP TO 1% TITANIUM, UP TO 1.%CARBON, AND THE BALANCE ESSENTIALLY NICKEL.
 2. A cold worked, dispersionstrengthened mechanically alloyed composition suitable for use in thefabrication of components for high temperature furnaces, said alloybeing characterized by a microstructure (i) substantially devoid of finegrains, (ii) in which the grains are coarse and elongated, and (iii) inwhich the aspect ratio of the grains is at least 5:1, said alloyconsisting essentially of about 12.5 to 18% chromium, about 0.175 toabout 0.45% yttria, the chromium and yttria being correlated so as torepresent a point falling within the area ABCD of the accompanyingdrawing, up to 1% aluminum, up to 1% titanium, up to 0.1% carbon and thebalance essentially nickel.
 3. An alloy in accordance with claim 2 inwhich the chromium and yttria are correlated so as to represent a pointfalling within the area EFGH of the accompanying drawing.
 4. As a newarticle of manufacture wire mesh belts for use in high temperaturefurnaces are formed from an alloy having a composition as set forth inclaim
 1. >